Electronic timing device



March 1l, 1952 w. D. HOUGHTON ELECTRONIC TIMING DEVICE Filed O01?. l 1947 F' .Za

7 HP W P Vw w .2 a MF ,L N w f ff, f m MMU 73 @Pw 75 f Lm N/ f w//Z mf 6 Pff if w PFW ff m ma w r @ma pw v j m n@ w., y/Mnwl 1 .1 met! LUG f A *l l M /f lllb IT HQ wm@ V me A *n j @E u [It M r v Q a a. Aolvumw da Z Patented Mar. 11, 1952 ELECTRONIC TIMING DEVICE William D. Houghton, Port Jefferson, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application October 1, 1947, Serial N o. 777,251 3 Claims. (Cl. Z50-27) This invention relates broadly to electric control circuits, and more specifically to an electronic timing device, sometimes referred to as an interval timer.

The present invention provides a method of and electronic apparatus for automatically opening and closing a circuit at any desired frequency ranging from less than 1 cycle per minute to over 120 cycles per minute. A feature of the invention comprises an arrangement which enables the ratio of closing to opening times to be continuously adjusted over any desired range up to 60% of the cyclic time interval.

A more detailed description of the invention follows in conjunction with a drawing, wherein:

Fig. 1 illustrates schematically the electrical circuit embodiment of the invention, and

Figs. 2a to 2d are curves given in explanation of the operation of the circuit of Fig. 1.

Referring to Fig. 1, the system of the invention comprises a pulse or blocking type of feedback oscillator A which drives or controls a selfrestoring flip-flop type of circuit B. This flipiiop circuit, is, in effect, an Eccles-Jordan type of self-restoring trigger circuit having a pair of vacuum tube electrode structures in which only one electrode structure at a time passes anode current.

Pulse oscillator A includes a triode vacuum tube 4 whose anode is connected through one winding a of a three-winding transformer T to the positive terminal +B of a source of unidirectional current I0. In circuit with the cathode of tube 4 and connected between the cathode and ground is the parallel combination of a potentiometer 5 and a by-pass condenser I. A bleeder resistor 2 is connected between the cat ode of tube 4 and the positive +B terminal. The grid of tube 4 is connected through the other two windings b and c (in series) of the transformer T to one end P of variable resistor 6. Windings b and c of transformer T are so connected that the voltage developed between point P and the grid of tube 4 is greater than the voltage developed across winding a. Resistor 6 is connected between positive terminal +B and ground through a serially arranged condenser 1.

The flip-flop or trigger circuit B comprises a pair of triode vacuum tube electrode structures I2 and I3, which although shown within separate evacuated envelopes may be contained within a single evacuated envelope. Only one tube at a time is conductive in this trigger circuit. In the stable state, tube I2 is nonconductive and tube I3 conductive.

voltage across condenser 'I.

In the active or tripped 56 windings.

state, tube I2 is conductive and tube I3 nonconductive. 'I'he anodes of tubes I2 and I3 are separately connected to the +B terminal of battery I0 through resistors 9- and II, respectively. The anode of tube I2 is connected to the grid of tube I3 through resistor 20. The grid of tube I3 is connected to ground through resistor I5. In eiect, resistors 2U and I5 may be considered a voltage divider. The cathode of tube I3 is connected through the operating winding of a load relay I6 to the cathode of tube I2. A common cathode resistor I4 is provided between ground and the cathode of tube I2. A resistor 8 is connected between the grid of tube I2 and the junction point P of resistor 6 and condenser 'I in the pulse or blocking type oscillator A.

Relay I6 in the cathode circuit of tube I3 of the ilip-op circuit B is provided with an armature II which is adapted to engage either of two oppositely disposed contacts I8 and I9. In the unenergized condition of this relay, the armature I1 engages contact I8 by virtue of the pressure exerted by a return spring 22.

As mentioned above, the flip-flop circuit B is so arranged that normally tube I2 is cut-01T (that is, biased to the anode current cut-01T condition), and tube I3 conducts, in which normal condition relay I6 will be energized and arma-- ture II will engage contact I9.

A detailed description of the operation of the electronic device of the invention will now be given:

The frequency of the pulse oscillator A is adjusted by means of potentiometer 6 whose adjusted value determines the rate of build-up of When the voltage across condenser 1 rises above the bias potential on tube 4, the bias potential being determined by the adjustment of variable resistor 5 in the cathode circuit, current starts to dow through the anode winding a of transformer T. This flow of current in winding a results in a voltage being developed across windings b and c. Windings a, b and c of transformer T are so poled that when the current in winding a increases, a positive voltage (positive with respect to the junction point P of condenser I and resistors 6 and yIl) is applied to the grid of tube 4. This positive voltage further increases the anode current in tube 4 which yflows through winding a and in turn further increases the positive voltage applied to the grid. This action continues until the voltage developed across condenser 1 approaches the voltage across the grid At this time the rate of change of anode current in tube 4 starts to decrease, as a result of which there is a decrease in grid voltage across the grid windings which, in turn, further decreases the anode current. This action continues until current through tube 4 ceases completely (that is, tube 4 is cut-off). When tube ll cuts-off, a negative voltage, approximately equal in magnitude to the voltage pulse developed across the grid windings b and c of transformer T, is present across condenser l. This voltage starts to rise, the rate of rise being determined by the time constant of resistor Ei and condenser 'I. By Varying the tap on variable resistor 6, the rate of voltage rise across condenser 'I is Varied and hence the repetition rate or frequency of the pulses produced by pulse oscillator A is varied. Stated in other words, during the time when the grid of tube 4 is positive, electron current flows from the grid of tube ll, through windings b and c of transformer T, and into condenser l, resulting in a charge being stored there-in. During the time interval when tube d is cut-oir, this charge starts to leak oir through resistor 6, resulting in a sawtooth wave being developed across condenser 'I as'shown in Figs. 2a and 2c. The rate at which this charge leaks off is a function of the lvalues of resistor 6 and condenser l. When the charge leaks olf to a Value such that the voltage at point P is slightly'less than the-bias applied to the cathode of tube (that is equal to the bias applied to tube less the cut-off potential of the tube used), it again starts to conduct causing condenser 'I to be recharged, thus starting a new cycle of operations.

The variable resistor located in the cathode circuit of ltube determines the potential with respect to ground at which tube 4 will start to conduct current. The bleeder resistor .2 increases the Voltage drop across resistor 5. In some cases this resistor may be eliminated. Condenser I is a bypass capacitor which maintains the voltage across resistor 5 constant by bypassing the a.-c components of cathode current. y

It will thus be appreciated that the amplitude of voltage change across condenser 'I is a function of the characteristics of transformer 'I and tube and the size of condenser 1. When resistor 5 is adjusted, this only changes the potential across condenser I with respect to ground at which tube Il starts to conduct; and hence changes the maximum negative and positive potential Vwhich is developed across condenser 'I, providing the potential developed across resistor 5,is small compared with the anode potential. That is, the peak-to-peak amplitude of the sawtooth voltagedeveloped across 'i does not appreciably change when resistor 5 is adjusted, whereas the D. C. voltage across I changes by an amount proportional to the voltage change across 5.

The waveforms of the voltage across condenser l for two conditions are shown in the curves of Figs. 2a and 2c. It should be noted that these waveforms are sawtooth in character. In Fig. 2a the bias developed across resistor 5 is such that the potential across condenser 'I rises to a slightly positive value with respect to ground before tube il conducts, and in Fig. 2c the tap on the cathode bias resistor is raised toward the cathode of tube Ll' and the voltage across condenser 'I rises to a value slightly less than zero before the tube I conducts.

Tube I2 of the ip-ilop circuit B is normally non-conductive (cut-off) due to the bias developed across resistor Il by the cathode current flowing in normally conductive tube I3. The normal cathode current of tube I3 is sufficient to operate relay I6 and close contacts I'l and I9. When the voltage on the grid of tube I2 rises to a point where tube I2 starts to conduct (due to the application of the sawtooth Waveform from the pulse oscillator A), the anode voltage of tube I2 starts to drop. As a result, the positive voltage applied to the grid of tube I3 starts to decrease, thereby causing the current in tube I3 to decrease. The decrease in current in tube I3 causes the biasing voltage developed across resistor Ill to decrease, which in `tur-n allows tube I2 to carry more current and hence reduce its anode potential to a still lower value. This action continues until tube I3 is completely cut-off and 4tube I2 is carrying full current.

Tube I2 remains in a conducting condition and causes tube I3 to remain non-conducting for the remainder of the appliedsawtooth wave. The result is that the relay IS remains in its de-energized state for this period and contacts I'I and I8 are engaged. In this condition the bias developed across resistor I4 by the current in tube I2 is sufficient to maintain tube I3 beyond'cut-oif.

YAt the end of the sawtooth wave (when the pulse-oscillator becomes operative and discharges l), the grid of tube I2 is suddenly reduced to a value which causes tube l2 to cease conducting and hence the bias voltage developed across resistor I4 by tube I2 is removed and also the positive voltage applied to the grid of tubeV I3 increases. Thus tube IB again establishes a bias across resistor III which causes tube I2 to be nonconductive.

Resistor vil in series with the grid of tube I2 limits the maximum grid-to-cathode potential of tube I2 to Zero and prevents the grid circuit of tube I2 Vfrom appreciably loading condenser V'I The value of resistor 9 is so chosen that a sufIicient amount of anode current iiows when tube l2 is conducting so as to maintain tube I3 cut-off.

Since a predetermined potential with respect to ground must be reached before tube I2 conducts, then by varying resistor 5 it is possible to make tube I2 conduct over a variable portion of the sawtooth voltage developed across condenser l. In this way a cha-nge in bias on thepulse oscillator will produce a change in the time of control of the flip-nop trigger circuit with vonly a negligible change in the frequency of the pulse oscillator.

In Figs. 2a and 2c, the dashed line indicates the tripping level of the nip-flop circuit B. It should be noted that the tripping potential is negative with respect to zero by the same amount in Figs. 2o. and 2c'. In the case of Fig. 2a, the flip-flop circuit B trips at a lower amplitude on the sawtooth waveform than in the case of Fig. 2c due to the sawtooth rising to a higher value in Fig. 2a than 4in Fig. 2c.

The anode current waveforms for tube I3 in the two cases of Figs. 2a and 2c are shown in Figs, 2b and 2d, respectively. Since the ow of current in tube I3 causes the relay I6 to operate, it will be seen that the waveforms of Figs. 2b and 2d also correspond to the operatingY times of relay I6. Time intervals t and t ofA Figs. 2b and 201Y thus represent the time intervals during which relayV I6 is operated and contacts I'I and I9 closed,

and t2 represent the time intervals during which relay I6 is unenergized and contacts I I and I8 closed.

Contacts I'I, I8 and I9 of relay I6 are connected to a suitable utilization circuit.

The system of the invention provides a means for energizing and de-energizing a relay coil which is used to close utilization circuits at the frequency of the pulse oscillator A. The ratio between energized time and de-energized time may be made continuously adjustable over ranges up to 60% of the cyclic period. A switch 2I is used to extend the range of this unit as follows: In normal operation the relay I6 may be made to be de-energized ior periods of time up to 60% of the cyclic period. In other words, contacts II and I8 may be engaged for periods of time ranging from 0 to 60% of the period of the pulse oscillator. With switch 2I in position X, terminal d is connected to terminal g through contacts II and I8 when the relay I6 is de-energized. Thus it is obvious that terminal d may be connected to y via contacts I1 and I8 for periods or time ranging from 0 to 60% of the period of pulse oscillator A. If it is desired to have these terminals connected together for longer periods of time, from 40% to 100% of the period, then switch 2| may be thrown to position Y and terminal d will be connected to terminal y via contacts I'I and I9 of relay 20.

This system may be used to control other electronic circuits by removing coil I6 and using the positive pulse developed across resistor II to drive such electronic circuits. It will be noted that a positive pulse of variable width and at a frequency determined by the design of pulse oscillator A is developed across resistor II.

What is claimed is:

1. An electronic timing system comprising a vacuum tube pulse oscillator circuit producing a repetitive sawtooth voltage, means for Varying the cut-off bias on said vacuum tube, a fiip-iiop circuit having a predetermined tripping level and coupled to and under control of said pulse oscillator, said flip-nop circuit having a normally nonconductive electrode structure and a normally conductive electrode structure interconnected regeneratively, a connection from said normally nonconductive electrode structure to said pulse oscillator circuit, whereby the Variation of the cut-oil bias on said vacuum tube varies the time at which said tripping level is reached by said sawtooth voltage, and a utilization circuit coupled to said normally conductive electrode structure.

2. An interval timing system comprising `a sawtooth voltage generator comprising a vacuum tube having anode, grid and cathode electrodes, a transformer having separate windings connected to said anode and grid, a variable bias resistor in the cathode circuit of said tube, a condenser in said generator across which the sawtooth voltage is produced, a nip-nop circuit having a predetermined tripping level and under control of while time intervals tI said sawtooth voltage generator, said flip-flop circuit including iirst and second electrode structures each including a grid, an anode and a cathode, means for Supplying polarizing potentials to the anodes of said structures, a connection including a current limiting resistor between the grid of said iirst structure and said condenser of the sawtooth voltage generator, whereby the variation of said bias resistor varies the time at which said tripping level is reached by said sawtooth voltage, a resistor between the anode of said rst structure and the grid of said second structure, a common resistor for the cathodes of said iirst and second structures, and a utilization circuit coupled to and controlled by the current ilow in said second electrode structure.

3. An interval timing system comprising a sawtooth voltage generator comprising a vacuum tube having anode, grid and cathode electrodes, a source of unidirectional potential, a transformer having a Winding between the positive terminal of said source and said anode, a variable bias resistor connected between said cathode and the negative terminal of said source, a condenser in series with a Variable resistor connected across said source, a pair of series connected windings of said transformer connected between said grid and the junction of said condenser and its serially arranged resistor, a nip-nop circuit under control of and tripped by said sawtooth voltage generator, said flip-flop circuit including a iirst normally non-conductive and a second normally conductive electrode structure each including a grid, an anode and a cathode, connections from the anodes of said structures to the positive terminal of said source, a connection including a current limiting resistor between the grid of said first structure and said junction, whereby the variation of said bias resistor affects the time of tripping of said iiip-iiop circuit, a resistor between the anode of said first structure and the grid of said second structure, a common resistor connecting the cathodes of said iirst and second structures to the negative terminal of said source, and a utilization circuit coupled to the cathode of said second structure and controlled by the current ilow in such structure.

WILLIAM D. HOUGHTON.

REFERENCES CITED The following references are of record in the le of this patent:

e UNITED STATES PATENTS Number Name Date 2,122,499 Stocker July 5, 1938 2,188,159 Rockwood Jan. 23, 1940 2,409,012 Bliss Oct. 8, 1946 2,414,486 Rieke Jan. 21, 1947 2,428,926I Bliss Oct. 14, 1947 2,434,894 Ambrose Jan. 27, 1948 2,427,497 Bartlett Mar. 9, 1948 2,442,238 Haungs May 25, 1948 

